Projective Varieties and Modular Forms Course Given at the Universit

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210 Martin Eichler UniversiUit Basel, Basel/Schweiz

Projective Varieties and Modular Forms Course Given at the University of Maryland, Spring 1970

Springer-Verlag Berlin· Heidelberg· New York 1971

AMS Subject Classifications (1970): l8G 10, 14M05, IOD 20

ISBN 3-54Q-55l9-3 Springer-Verlag Berlin . Heide1bt:rg . New York ISBN 0-38H)5519-3 Springer-Verlag New York· Heidelberg· Berlin This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other than private use, a fee is payable to the publisher, the amount of the fee to be determined by agreement with the publisher. © by Springer-Verlag Berlin· Heidelberg 1971. Library of Congress Catalog Card Number 78-166998.

Offsetdruck: Julius Beitz, HemsbachlBergstr.

CONTENTS Introduction • . • • • .

1

Chapter I

4

Graded Modules

§l.

Some basic concepts

4

§2.

Free resolutions

9

3.

The functors

§4.

The functors

§5.

Modules over polynomial rings

§ 6.

The rank polynomial. .

§7.

Reduction of the number of variables



§ 8.

Structural properties.

• • 34

§9.

The theorem of Riemann-Roch and the duality theorem • • • 39

§

Chapter II

· • 13 18

continued

21 • 26

Graded Rings and Ideals •

• 3a

49

§10.

Introduction, divisors

§ll.

Differentials and the theorem of Riemann-Roch .

• 55

§l2.

Automorphic forms and projective varieties.

• 63

§13.

Quasiinvertible ideals

67

§14.

Intersection numbers

72

§15.

Regular local rings.

79

Chapter III

49

88

Applications to Modular Forms.

§l6.

Introduction

88

§l7.

Specializations of modular forms

91

§l8.

Principal ideals

§l9.

Hilbert modular forms in 2 variables . •

Appendix

..

Conjectures and Problems

I-

..

..

..











..











..



...

...









• 97

100

..

..



oil





II

II

115

INTRODUCTION

W.L. BaiZy and A. BoreZ showed (Compactification of arithmetic quotients of bounded symmetric domains, Annals of Math. 84(1966), p. 442-528) that the graded rings of automorphic forms are finitely generated, provided that rather general conditions are satisfied.

Let

be a system of generators, then between the Y. some poly~

nomial equations

Fv(yo,···.ym)

=

0

will hold. and all these equations

are consequences of finitely many of them.

Let us assume for the sake

of simplicity (although it is wrong in general) that the Y same weights.

i

have the

Then the F (y.) are homogeneous polynomials, and their

v

~

zeros form a projective variety Gn in the projective space pm with the coordinates Yi' whose dimension is

n < m.

Projective varieties

are the most common examples of algebraic varieties although it can be shown that there exist (rather exceptional) algebraic varieties which are not projective.

The theorem of Baily and Borel opens the way to

an al